H, W, N, K = map(int, input().split())
if H == 1:
    print("YES" if (W - 1) % N == K - 1 else "NO")
    exit()
if W == 1:
    print("YES" if (H - 1) % N == K - 1 else "NO")
    exit()

print("YES" if ((H - 1) * (W - 1) + 1) % N == K - 1 else "NO")